1. Technical Field
The technical field relates generally to motor vehicle controller area networks and, more particularly, to modification of the communication strategy for hybrid vehicles to avoid conflicting responses by controllers to messages broadcast on the network bus.
2. Description of the Problem
Hybrid vehicles are generally equipped with at least two prime movers for developing mechanical power. One prime mover may be a dual function system that can develop mechanical power both for traction or power for take-off (PTO) equipment and which can be backdriven as a step in the conversion of mechanical energy to potential energy for storage. An electric traction motor which can be used for regenerative braking of the vehicle to generate electricity is suitable as such a prime mover, as are pneumatic and hydraulic accumulator based systems and mechanical fly wheels. The other prime mover is typically a thermal engine such as an internal combustion engine (ICE) which may supply mechanical power for traction, to backdrive the electric traction motor for the generation of electricity, to run a generator, and may be able to provide non-regenerative vehicle braking (e.g., engine or “Jake” brakes). The internal combustion engine for a hybrid-ICE/electric vehicle will be called on to carry out at least one of the listed functions and in some parallel type hybrid vehicles will perform more than one.
The development of vocational commercial truck chassis configured with hybrid electric drive systems which can propel the vehicle as well as provide angular velocity to PTO equipment has increased the complexity of integration of the chassis's systems (and subsystems), the hybrid electric system and installed PTO equipment, particularly on parallel type hybrid vehicles. One consequence of this increased complexity is reflected in the potential for increased data traffic on the controller area network [CAN] relating to managing the variable rate of change in the angular velocity and moment of inertia of the thermal/internal combustion engine under the management of an engine controller. Multiple controllers or “nodes” on the CAN can be the source of torque/speed requests to which the engine controller is programmed to respond. Among the possible sources of such broadcasts are a transmission controller, an ABS controller, a body controller, and a hybrid controller. The messages generated by the different sources can easily be in conflict with one another with respect to changes in angular speed and torque requested from the thermal engine.
Conflicts in the timing of messages are handled through a control strategy referred to as, “non-destructive bit wise arbitration”. Arbitration priorities contained in the CAN message structure establish which among conflicting messages has priority to the serial communication bus of the network. If the source of the speed/torque message has a high enough arbitration priority (i.e., a low absolute numeric value), and the other node(s) on the CAN bus with a higher priorities are not in direct conflict with the immediate source, then the controller for the thermal engine responds to the speed/torque message and adjusts the output of the thermal engine accordingly. However, the lower priority node may attempt to broadcast its request following handling of the original request. Where the follow up message changes the result from the original message, variation in the thermal engine's output can result. In addition, data traffic on the serial communication bus can began to increase with data traffic, particularly relating to operation of the thermal engine, but affecting access to the bus generally.
A parallel hybrid vehicle with PTO capability greatly increases the chances for conflicting requests for changes in thermal engine angular speed and torque messages. For example, in a conventional (non-hybrid) vehicle, if the operator of the vehicle desires to increase the thermal engine's angular velocity by the means of a remotely mounted engine speed control device, he could do so through a sensor connected to the body controller which would in turn process and condition the input data as output data for broadcast on the CAN bus as a speed/torque message. A vehicle “up-fitted” for hybrid operation with an electric traction motor/generator which can act as a prime mover in conjunction with the thermal engine to supply angular velocity and torque changes the issue. In this configuration both the hybrid controller and the thermal engine controller will have the task of “co-managing” operation of the thermal engine to adjust the output of the thermal engine depending upon the availability of speed or torque from the electric traction motor/generator. This co-management strategy can become very complex considering the many real time transitions which will take place requiring the thermal engine to act as the prime mover exclusively (the motor/generator operating to charge the battery pack under power from the thermal engine) or the hybrid electric traction motor/generator acting as the prime mover supporting electrified power take off (ePTO) operation.